"Felsenmeer" is a german word for "sea of rocks". The Blue Hills felsenmeer is the most famous in the area and was created at the time of the last glaciation. Felsenmeers are formed when large boulders shatter in place due to freezing/thawing. It is 82 feet deep and 1000 ft long. The air in the valley bottom is several degrees cooler. Because of the unique geology and plants growing there the Felsenmeer has been a State Natural Area since 1969. No logging and vehicles are allowed on the 75 acres.